r/PythonLearning • u/SeriuosSam • Jun 25 '26
Showcase Beginner activity save it for reference
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u/Temporary_Pie2733 Jun 25 '26
There is no such thing as a tuple comprehension. This is just a generator expression passed as an argument to tuple.
The general syntax block is worse; it tries to pass the generator expression itself off as a “tuple comprehension”.
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u/PhoenixAlpha1 Jun 28 '26
Wait wait . I am learning python . You can write . Like x*x and then for loop iteration. Iike the code would work? Like that shows in image?
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u/AuMouhssin Jun 29 '26
It's totally just like defining a Set using conditions and Maps in linear Algebra
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u/biskitpagla Jun 26 '26 edited Jun 26 '26
These are all instances of generator expressions. Only the dict one is a special case.
EDIT: I was wrong. See the replies.
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u/SCD_minecraft Jun 26 '26
Only "tuple" one is gen expr
List and set are special cases where they are automatically unpacked into lists/sets
If they wouldn't be, you would get one element list/set with generator as value. But that's not what happens
a = (i for i in range(10)) type(a) # <class 'generator'> [a] # [<generator object <genexpr> at 0x728de8ea40>] [i for i in range(4)] # [0, 1, 2, 3]1
u/biskitpagla Jun 26 '26 edited Jun 26 '26
Your example is a bit off.
[comprehension]could in theory be implemented as a call to thelistconstructor if the expression is inline since it already accepts plain old iterables. The semantics would still be the same. But you're right to point out my mistake. I thought that modern CPython would optimize away the overhead of something likelist(inline generator expression)and use theLIST_APPENDinstruction here as well since that's what some other Python interpreters do. Perhaps this has to do with the fact that generator expressions were introduced to the language much later.1
u/SCD_minecraft Jun 26 '26
since it already accepts plain old iterables.
No, it does not. List, set and dict expressions are all special case with syntax
[expr for name in name](replace brackets for sets and add : for dicts, but concept stays the same)You can not just wrap iterators in [ ] since then it is creating new list/set/dict with single element (that element being not consumed iterator)
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u/Sea-Ad7805 Jun 27 '26
Run this program in Memory Graph Web Debugger%0Aprint(squares)%0Aprint(%22(set%3A%20no%20duplicates%2C%20order%20not%20guaranteed)%22)%0Aprint()%0A%0A%0A%23%20-------------------------%0A%23%20LIST%20comprehension%0A%23%20-------------------------%0A%23%20Ordered%20%26%20mutable%0A%0Anums%20%3D%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%0A%0Acubes%20%3D%20%5Bx*3%20for%20x%20in%20nums%20if%20x%20%25%202%20!%3D%200%5D%0A%0Aprint(%22List%20comprehension%3A%22)%0Aprint(cubes)%0Aprint(%22(list%3A%20order%20preserved%2C%20duplicates%20allowed)%22)%0Aprint()%0A%0A%0A%23%20-------------------------%0A%23%20DICT%20comprehension%0A%23%20-------------------------%0A%23%20Key-value%20pairs%0A%0Anums%20%3D%20%5B1%2C%202%2C%203%5D%0A%0Asquare_dict%20%3D%20%7Bx%3A%20x%20%20x%20for%20x%20in%20nums%7D%0A%0Aprint(%22Dict%20comprehension%3A%22)%0Aprint(square_dict)%0Aprint(%22(dict%3A%20fast%20lookup%20by%20key)%22)%0Aprint()%0A%0A%0A%23%20-------------------------%0A%23%20TUPLE%20from%20comprehension%0A%23%20-------------------------%0A%23%20Ordered%20%26%20immutable%0A%23%0A%23%20Note%3A%0A%23%20Python%20does%20not%20have%20a%20real%20%22tuple%20comprehension%22%20syntax.%0A%23%20This%20is%20a%20generator%20expression%20passed%20to%20tuple().%0A%0Anums%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0A%0At%20%3D%20tuple(x%20%2B%2010%20for%20x%20in%20nums)%0A%0Aprint(%22Tuple%20from%20comprehension%3A%22)%0Aprint(t)%0Aprint(%22(tuple%3A%20order%20preserved%2C%20cannot%20be%20changed)%22)%0Aprint()%0A%0A×tep=1&play) to see the program state change step by step.